In a previous exercise, I developed a defect tracker application and, because I did not want others making code changes, I released only the MDE version. As you noticed, the major drawback is that the end user cannot add new reports to an MDE version. An alternative is create a distinct but related "report" application.
An MS Access application is a database and can be referenced by another MS Access application. The steps involved in enhancing the reports capability are:
• create/open a new MS Access application (e.g., Business Reports);
• rather than creating any tables, link the tables from the main application to the new application
File -> Get External Data -> Link Tables …
• select the main application (or the LDB file if the application and data were segregated) from where you want the data
• 'Link Tables" window is shown with a list of data tables found within the application
• that window, click on the 'Select All' button and then the 'OK' button
The new application should now have access to all of the data tables and additional forms and/or reports can be developed by the user to fit their needs. This also allows you to keep the main application "pure" while still providing the user with reporting flexibility. Depending on the usage of the application, you probably still need to view the user designed report and query SQL statements to ensure that a user has not included an instance that dramatically reduces the system responsiveness.